1. Field of the Invention
The present invention relates to a method for data transmission via an electric distribution system and to a transmission system for carrying out the method.
2. Discussion of Background
Electric distribution systems which, as a rule, comprise a high-voltage distribution line, a medium-voltage distribution line and a low-voltage distribution line with the corresponding service connections, have long been used as a medium for transmitting data, particularly for the purposes of the electricity supply companies involved.
Thus it is known, for example from the journals BBC-Nachrichten, Volume 8/9, 1977, pages 388 to 395, to use the medium- or high-voltage distribution line of the distribution system as a transmission path for building up so-called multiservice control systems in which control commands are conducted from the electricity supply companies to the consumers.
In such an information transmission system, problems arise for transmission from one level of the distribution system to another distribution line since between the distribution lines appropriate transformers are arranged which, being large inductances, inhibit in particular the propagation of higher frequencies.
The disadvantageous influence of the transformers can be avoided, on the one hand, by connecting in parallel with the transformer a communications bypass which in each case receives the data before the transformer, regenerates them and feeds them in again after the transformer. However, such a bypass solution is very complex, particularly between the medium- and low-voltage distribution line since this includes a plurality of transformers all of which must be bridged if the data transmission is to extend right up to the service connections.
On the other hand, it is possible to transmit data through these transformers with correspondingly low frequencies. However, this has the disadvantage that transmission in the frequency range in question is impaired by strong low-frequency noise containing, above all, harmonics of the power-system frequency.
Data transmission via the medium-voltage distribution line to the individual service connections is therefore possible only with great effort or with low protection against interference in the case of the known solutions.